1. Field of the Invention
Inflatable devices for occupant restraint in vehicles or aircraft have been under development worldwide for many years. Patents have been granted on numerous gas generating compositions for inflating occupant restraint devices. Because of the strict requirements related to the nontoxic nature of the inflating gases most, if not all, gas generants now in use are based on azides, and especially sodium azide.
The use of sodium azide (or other azides) results in extra expense and risk in gas generant manufacture due to the extreme toxicity of azides. In addition, the potential hazard and disposal problem of unfired inflation devices must be considered. A nonazide containing gas generant is believed to provide significant advantages over an azide-based gas generant because of these toxicity related concerns.
An additional problem with azide-based gas generants is that they are relatively poor gas producers. Sodium azide, the primary gas source in azide-based gas generants, consists of only 64.6% nitrogen. In order to make a useful gas generant, however, other materials, such as oxidizers and slag formers must be added to the sodium azide. These additives produce little or no gas and therefore reduce the overall yield of gas to approximately 40 to 55% by weight (or approximately 1.3 to 2.0 moles of gas per 100 grams of gas generant).
The nongaseous fraction (45 to 60%) of the gas generant products must be contained or filtered in order to provide a clean inflating gas. This filter requires additional volume thereby increasing the size of the gas generator. The large fraction of nongaseous material is very hot and by remaining in the gas generator causes the gas generator to become hot and can result in a "soak back" temperature problem.
There are, therefore, several advantages to gas generants which produce more gas and less solids. Several attempts have been made to solve the problems mentioned above by the use of azide-free gas generants.
2. Description of the Prior Art
The compositions described in U.S. Pat. Nos. 4,909,549 and 4,948,439 describe the use of tetrazole or triazole compounds in combination with metal oxides and oxidizer compounds (alkali metal, alkaline earth metal, and ammonium nitrates or perchlorates) as gas generant compositions.
The compositions described in U.S. Pat. No. 5,035,757 result in more easily filterable solid products but the gas yield is without substantial improvement.
U.S. Pat. No. 3,954,528 describes the use of triaminoguanidine nitrate ("TAGN") and a synthetic polymeric binder in combination with an oxidizing material. The oxidizing materials include ammonium nitrate ("AN") although the use of phase stabilized ammonium nitrate ("PSAN") is not suggested. The patent teaches the preparation of propellants for use in guns or other devices where large amounts of carbon monoxide and hydrogen are acceptable and desirable.
U.S. Pat. No. 3,044,123 describes a method of preparing solid propellant pellets containing AN as the major component. The method requires use of an oxidizable organic binder (such as cellulose acetate, PVC, PVA, acrylonitrile and styrene-acrylonitrile), followed by compression molding the mixture to produce pellets and by heat treating the pellets. These pellets would certainly be damaged by temperature cycling because commercial AN is used and the composition claimed would produce large amounts of carbon monoxide.
U.S. Pat. No. 5,034,072 is based on the use of 5-oxo-3-nitro-1,2,4-triazole as a replacement for other explosive materials (HMX, RDX, TATB, etc.) in propellants and gun powders. This compound is also called 3-nitro-1,2,4-triazole-5-one ("NTO"). The claims appear to cover a gun powder composition which includes NTO, AN and an inert binder. Although called inert, the binder would enter into the combustion reaction and produce carbon monoxide making it unsuitable for air bag inflation.
U.S. Pat. No. 5,197,758 describes gas generating compositions comprising a non-azide fuel which is a transition metal complex of an aminoarazole, and in particular are copper and zinc complexes of 5-aminotetrazole and 3-amino-1,2,4-triazole which are useful for inflating airbags in automotive restraint systems.
In addition to U.S. Pat. Nos. 5,035,757 and 3,954,528 described herein-above the following U.S. Patents were cited in application Ser. No. 07/867,439 of which the present application is a continuation-in-part.
U.S. Pat. No. 4,931,112 describes an automotive airbag gas generant formulation consisting essentially of NTO (5-nitro-1,2,4-triazole-3-one) and an oxidizer wherein said formulation is anhydrous.
U.S. Pat. No. 4,601,344 describes a gas generating composition containing glycidyl azide polymer and a high nitrogen content additive which generates large amounts of nitrogen gas upon burning and is useful to extinguish fires.
U.S. Pat. No. 4,234,363 describes a solid propellant hydrogen generator comprising an oxidizer, a fuel, and a binder such as a polyester binder said generator being useful for chemical laser systems.
U.S. Pat. No. 4,111,728 describes gas generators for inflating life rafts and similar devices or useful as rocket propellants comprising ammonium nitrate, a polyester type binder and a fuel selected from oxamide and guanidine nitrate.
U.S. Pat. No. 4,124,368 describes a method for preventing detonation of ammonium nitrate by using potassium nitrate.
U.S. Pat. Nos. 4,552,736 and 5,098,683 describe the use of potassium fluoride to eliminate expansion and contraction of ammonium nitrate in transition phase.
U.S. Pat. No. 5,074,938 describes the use of phase stabilized ammonium nitrate as an oxidizer in propellants containing boron and useful in rocket motors.
U.S. Pat. No. 4,925,503 describes an explosive composition comprising a high energy material, e.g., ammonium nitrate and a polyurethane polyacetal elastomer binder the latter component being the focus of the invention.
U.S. Pat. No. 3,071,617 describes long known considerations as to oxygen balance and exhaust gases.
U.S. Pat. No. 4,300,962 describes explosives comprising ammonium nitrate and an ammonium salt of a nitroazole.
U.S. Pat. No. 3,719,604 describes gas generating compositions comprising aminoguanidine salts of azotetrazole or of ditetrazole.
U.S. Pat. No. 5,034,072 describes the use of 5-oxo-3-nitro-1,2,4-triazole, nitrocellulose and a liquid nitric ester for making gun powder said composition being less hygroscopic than a propellant containing ammonium nitrate.
U.S. Pat. No. 5,125,684 describes an extrudable propellant fuour use in crash bags comprising an oxidizer salt, a cellulose-based binder and a gas generating component.
U.S. Pat. No. 5,139,588 describes non-azide gas generants useful in automotive restraint devices comprising a fuel, an oxidizer and additives.